The overall goal of this proposal is to determine the extent to which prenatal factors influence predisposition to obesity in children. A series of longitudinal observations are proposed, beginning in the fetal period and continuing through the first year life, in two models of human obesity: 1) offspring of mothers with gestational diabetes (non-insulin treated, non-obese); and, 2) offspring of mothers who are obese before pregnancy (non-diabetic). These two groups will be compared to children of no-obese non-gestational diabetic controls. The specific aims are: 1) To examine whether prenatal factors, including gestational diabetes and maternal obesity, influence fetal and neonatal body composition, neonatal energy expenditure and endocrine profile; and, 2) To examine the relationship between neonatal body composition, energy expenditure, and umbilical cord blood endocrine profile with the development of obesity at one year of age. Energy expenditure will be measured in infants using doubly labeled water and in mother using a 3 compartment model combining underwater weight and total body water and in infants using a combination of total body electrical conductivity and total body water. The hypothesis to be tested are: 1) The prenatal environment IS involved in the predisposition to obesity in gestationally diabetic mothers but NOT in obese mothers where the familial environment, including inherited tendencies, contributes to pre-disposition to obesity; and, 2) The prenatal environment associated with gestational diabetes is related to chronic and persisting alterations in energy metabolism that contribute to a pre-disposition to obesity. The significance of these pilot and feasibility studies is to lay the groundwork for studies which will focus on identifying maternal interventions (examples: maternal exercise, maternal insulin administration, maternal dietary management) that can modify the prenatal environment in a manner that will protect newborns from developing obesity later in life.